Thermogravimetric and H-1 NMR spectroscopy studies of water on silicalites

A study has been made of two silicalite samples with a specific surface (by BET method) S = 312 and 244 m(2) g(-1) that were synthesised on the basis of fumed silica and did not contain aluminium. The H-1 NMR spectroscopy and thermogravimetric methods were used to characterise adsorbed water layers. It has been found that in the case of both water vapour adsorption and wat er adsorption from aqueous suspensions the volume of silicalite pores occup ied by adsorbed water molecules is considerably smaller than the total volu me of pores. The chemical shift of water molecules on the silicalite surfac e depends on temperature and varies from 4.5 ppm at 330 K to 5.6 ppm at 220 K. The high chemical shift values are attributed to clustering of water mo lecules in the adsorbent pores and to the fact that each molecule of the cl usters at the same time participates in the formation of more than three hy drogen bonds. (C) 1999 Elsevier Science B.V. All rights reserved.